After graduation, Heder moved to Hollywood to become an actress and screenwriter while working for a nanny agency. At the agency, she worked for guests with children staying at four-star hotels and her experiences inspired her first short film.[3]

In 2010 Heder won a Peabody Award, along with her fellow writers, for her work on the acclaimed U.S. television series, Men of a Certain Age.[6] In 2011 she wrote and directed a short comedy, Dog Eat Dog (A Short Tale) starring Zachary Quinto[7] to raise awareness for pet adoption, and that short film can be watched for free on YouTube. She wrote for seasons 1-3 of the Netflix original series Orange Is the New Black before taking time off from that job to direct the film Tallulah.

In 2015, Sian Heder directed Tallulah, starring Ellen Page and Allison Janney.[8]Tallulah was backed by Route One Entertainment, Maiden Voyages Pictures and Ocean Blue Entertainment. The film was set to premier as one of 65 films selected for Sundance Film Festival January 21–31 in Utah.[9] Netflix obtained worldwide rights to stream Tallulah in January 2016. The film received positive reviews from critics,[10] and was released on July 29, 2016.[11][12]